Reduction of the efficiency of photoinduced polymerisation in C60 films on irradiation with femtosecond laser pulses

Photopolymerisation of oxygen-bearing C₆₀ films by λ = 459 nm laser radiation and by 100-fs λ = 410 nm pulses was compared by visual observation of photodarkening spots and by recording the Raman spectra, in the range 600 — 1700 cm^–1, of the irradiated regions. When the average intensity was 10 — 20 W cm^–2, the irradiation dose needed for photopolymerisation was very different in the cw and pulsed cases. For the cw radiation, it was close to the dose for oxygen-free samples, amounting to 20 kJ cm^–2. For the femtosecond pulses, the threshold radiation dose was two orders of magnitude higher, which could be attributed to characteristic features of relaxation of the excited molecules.